One of the mistakes made by the positivists in classification is the claim that their favorite system can be applied to all libraries alike. That this is a fallacy may be seen in an example or two. Take the case of a large and comprehensive Botanical library, in which an exact scientific distribution of the books may and should be made. It is classified not only in the grand divisions, such as scientific and economic botany, etc., but a close analytical treatment is extended over the whole vegetable kingdom. Books treating of every plant are relegated to their appropriate classes, genera, and species, until the whole library is organised on a strictly scientific basis. But in the case, even of what are called large libraries, so minute a classification would be not only unnecessary, but even obstructive to prompt service of the books. And the average town library, containing only a shelf or two of botanical works, clearly has no use for such a classification. The attempt to impose a universal law upon library arrangement, while the conditions of the collections are endlessly varied, is foredoomed to failure. The object of classification is to bring order out of confusion, and to arrange the great mass of books in science and literature of which every library is composed, so that those on related subjects should be as nearly as possible brought together. Let us suppose a collection of some hundred thousand volumes, in all branches of human knowledge, thrown together without any classification or catalogue, on the tables, the shelves, and the floor of an extensive reading-room. Suppose also an assemblage of scholars and other readers, ready and anxious to avail themselves of these literary treasures, this immense library without a key. Each wants some certain book, by some author whose name he knows, or upon some subject upon which he seeks to inform himself. But how vain and hopeless the effort to go through all this chaos of learning, to find the one volume which he needs! This illustration points the prime necessity of classification of some kind, before a collection of books can be used in an available way. Then comes in the skilled bibliographer, to convert this chaos into a cosmos, to illumine this darkness with the light of science. He distributes the whole mass, volume by volume, into a few great distinct classes; he creates families or sub-divisions in every class; he assembles together in groups all that treat of the same subject, or any of its branches; and thus the entire scattered multitude of volumes is at length cooerdinated into a clear and systematic collection, ready for use in every department. A great library is like a great army: when unorganized, your army is a mere undisciplined mob: but divide and sub-divide it into army corps, divisions, brigades, regiments, and companies, and you can put your finger upon every man.